source: Sophya/trunk/SophyaExt/XephemAstroLib/mooncolong.c@ 2755

/* code to compute lunar sunrise position and local sun angle.
 */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include "astro.h"

static void Librations (double RAD, double LAMH, double BH, double OM,
    double F, double L, double L1, double *L0, double *B0);
static void Moon (double RAD, double T, double T2, double LAM0, double R,
    double M, double *F, double *L1, double *OM, double *LAM, double *B,
    double *DR, double *LAMH, double *BH);
static void Sun (double RAD, double T, double T2, double *L, double *M,
    double *R, double *LAM0);

/* given a Julian date and a lunar location, find selenographic colongitude of
 * rising sun, lunar latitude of subsolar point, illuminated fraction, and alt
 * of sun at the given location. Any pointer may be 0 if not interested.
 * From Bruning and Talcott, October 1995 _Astronomy_, page 76.
 * N.B. lunar coordinates use +E, but selenograhic colongs are +W.
 */
void
moon_colong (
double jd,      /* jd */
double lt,      /* lat of location on moon, rads +N +E */
double lg,      /* long of location on moon, rads +N +E */
double *cp,     /* selenographic colongitude (-lng of rising sun), rads */
double *kp,     /* illuminated fraction of surface from Earth */
double *ap,     /* sun altitude at location, rads */
double *sp)     /* lunar latitude of subsolar point, rads */
{
        double RAD = .0174533;
        double T;
        double T2;
        double L, M, R, LAM0;
        double F, L1, OM, LAM, B, DR, LAMH, BH;
        double L0, B0;
        double TEMP;
        double C0;
        double PSI;
        double NUM, DEN;
        double I, K;
        double THETA, ETA;
        double H;

        T = (jd - 2451545)/36525.0;
        T2 = T * T;

        Sun(RAD, T, T2, &L, &M, &R, &LAM0);
        Moon(RAD, T, T2, LAM0, R, M, &F, &L1, &OM, &LAM, &B, &DR, &LAMH, &BH);
        Librations(RAD, LAMH, BH, OM, F, L, L1, &L0, &B0);
        if (sp)
            *sp = B0;

        TEMP = L0 / 360;
        L0 = ((TEMP) - (int)(TEMP)) * 360;
        if (L0 < 0) L0 = L0 + 360;
        if (L0 <= 90) C0 = 90 - L0; else C0 = 450 - L0;
        if (cp) {
            *cp = degrad(C0);
            range (cp, 2*PI);   /* prefer 0..360 +W */
        }

        if (kp) {
            TEMP = cos(B * RAD) * cos(LAM - LAM0 * RAD);
            PSI = acos(TEMP);
            NUM = R * sin(PSI);
            DEN = DR - R * TEMP;
            I = atan(NUM / DEN);
            if (NUM * DEN < 0) I = I + 3.14159;
            if (NUM < 0) I = I + 3.14159;
            K = (1 + cos(I)) / 2;
            *kp = K;
        }

        if (ap) {
            THETA = lt;
            ETA = lg;
            C0 = C0 * RAD;
            TEMP = sin(B0) * sin(THETA) + cos(B0) * cos(THETA) * sin(C0+ETA);
            H = asin(TEMP);
            *ap = H;
        }
}

static void
Librations (double RAD, double LAMH, double BH, double OM, double F,
double L, double L1, double *L0, double *B0)
{ 
        double I, PSI, W, NUM, DEN, A, TEMP;

        /* inclination of lunar equator */
        I = 1.54242 * RAD;

        /* nutation in longitude, in arcseconds */
        PSI = -17.2 * sin(OM) - 1.32 * sin(2 * L) - .23 * sin(2 * L1) +
                                                            .21 * sin(2 * OM);
        PSI = PSI * RAD / 3600;

        /* optical librations */
        W = (LAMH - PSI) - OM;
        NUM = sin(W) * cos(BH) * cos(I) - sin(BH) * sin(I);
        DEN = cos(W) * cos(BH);
        A = atan(NUM / DEN);
        if (NUM * DEN < 0) A = A + 3.14159;
        if (NUM < 0) A = A + 3.14159;
        *L0 = (A - F) / RAD;
        TEMP = -sin(W) * cos(BH) * sin(I) - sin(BH) * cos(I);
        *B0 = asin(TEMP);
}

static void
Moon (double RAD, double T, double T2, double LAM0, double R, double M,
double *F, double *L1, double *OM, double *LAM, double *B, double *DR,
double *LAMH, double *BH)
{
        double T3, M1, D2, SUMR, SUML, DIST;

        T3 = T * T2; 

        /* argument of the latitude of the Moon */
        *F = (93.2721 + 483202 * T - .003403 * T2 - T3 / 3526000) * RAD;

        /* mean longitude of the Moon */
        *L1 = (218.316 + 481268. * T) * RAD;
        
        /* longitude of the ascending node of Moon's mean orbit */
        *OM = (125.045 - 1934.14 * T + .002071 * T2 + T3 / 450000) * RAD;
        
        /* Moon's mean anomaly */
        M1 = (134.963 + 477199 * T + .008997 * T2 + T3 / 69700) * RAD;
        
        /* mean elongation of the Moon */
        D2 = (297.85 + 445267 * T - .00163 * T2 + T3 / 545900) * 2 * RAD;

        /* Lunar distance */
        SUMR = -20954 * cos(M1) - 3699 * cos(D2 - M1) - 2956 * cos(D2);
        *DR = 385000 + SUMR;
        
        /* geocentric latitude */
        *B = 5.128 * sin(*F) + .2806 * sin(M1 + *F) + .2777 * sin(M1 - *F) +
                                                        .1732 * sin(D2 - *F);
        SUML = 6.289 * sin(M1) + 1.274 * sin(D2 - M1) + .6583 * sin(D2) +
                .2136 * sin(2 * M1) - .1851 * sin(M) - .1143 * sin(2 * *F);
        *LAM = *L1 + SUML * RAD;
        DIST = *DR / R;
        *LAMH = (LAM0 + 180 + DIST * cos(*B) * sin(LAM0 * RAD - *LAM) / RAD)
                                                                        * RAD;
        *BH = DIST * *B * RAD;
}

static void
Sun (double RAD, double T, double T2, double *L, double *M, double *R,
double *LAM0)
{
        double T3, C, V, E, THETA, OM;

        T3 = T2 * T;

        /* mean longitude of the Sun */
        *L = 280.466 + 36000.8 * T;

        /* mean anomaly of the Sun */
        *M = 357.529 + 35999 * T - .0001536 * T2 + T3 / 24490000;
        *M = *M * RAD;

        /* correction for Sun's elliptical orbit */
        C = (1.915 - .004817 * T - .000014 * T2) * sin(*M) +
                    (.01999 - .000101 * T) * sin(2 * *M) + .00029 * sin(3 * *M);

        /* true anomaly of the Sun */
        V = *M + C * RAD;

        /* eccentricity of Earth's orbit */
        E = .01671 - .00004204 * T - .0000001236 * T2;

        /* Sun-Earth distance */
        *R = .99972 / (1 + E * cos(V)) * 145980000;

        /* true geometric longitude of the Sun */
        THETA = *L + C;

        /* apparent longitude of the Sun */
        OM = 125.04 - 1934.1 * T;
        *LAM0 = THETA - .00569 - .00478 * sin(OM * RAD);
}

#ifdef TESTCOLONG

/* insure 0 <= *v < r.
 */
void
range (v, r)
double *v, r;
{
        *v -= r*floor(*v/r);
}

/* To be sure the program is functioning properly, try the test case
 * 2449992.5 (1 Oct 1995): the colongitude should be 3.69 degrees.
 */
int
main (int ac, char *av[])
{
        double jd, lt, lg;
        double c, k, a;

        if (ac != 2) {
            fprintf (stderr, "%s: JD\n", av[0]);
            abort();
        }

        jd = atof(av[1]);

        printf ("Latitude of lunar feature: ");
        fscanf (stdin, "%lf", &lt);
        lt = degrad(lt);
        printf ("Longitude:                 ");
        fscanf (stdin, "%lf", &lg);
        lg = degrad(lg);

        moon_colong (jd, lt, lg, &c, &k, &a);

        printf ("Selenographic colongitude is %g\n", raddeg(c));
        printf ("The illuminated fraction of the Moon is %g\n", k);
        printf ("Altitude of Sun above feature is %g\n", raddeg(a));

        return (0);
}

#endif

/* For RCS Only -- Do Not Edit */
static char *rcsid[2] = {(char *)rcsid, "@(#) $RCSfile: mooncolong.c,v $ $Date: 2005-01-17 10:13:05 $ $Revision: 1.4 $ $Name: not supported by cvs2svn $"};